1. Field of the Invention
The present invention generally relates to the field of fiber production. More specifically, the invention relates to fibers of micron and sub-micron size diameters.
2. Description of the Relevant Art
Fibers having small diameters (e.g., micrometer (“micron”) to nanometer (“nano”)) are useful in a variety of fields from the clothing industry to military applications. For example, in the biomedical field, there is a strong interest in developing structures based on nanofibers that provide scaffolding for tissue growth to effectively support living cells. In the textile field, there is a strong interest in nanofibers because the nanofibers have a high surface area per unit mass that provide light, but highly wear resistant, garments. As a class, carbon nanofibers are being used, for example, in reinforced composites, in heat management, and in reinforcement of elastomers. Many potential applications for small-diameter fibers are being developed as the ability to manufacture and control their chemical and physical properties improves.
It is well known in fiber manufacturing to produce extremely fine fibrous materials of organic fibers, such as described in U.S. Pat. Nos. 4,043,331 and 4,044,404, where a fibrillar mat product is prepared by electrostatically spinning an organic material and subsequently collecting spun fibers on a suitable surface; U.S. Pat. No. 4,266,918, where a controlled pressure is applied to a molten polymer which is emitted through an opening of an energy charged plate; and U.S. Pat. No. 4,323,525, where a water soluble polymer is fed by a series of spaced syringes into an electric field including an energy charged metal mandrel having an aluminum foil wrapper there around which may be coated with a PTFE (Teflon™) release agent. Attention is further directed to U.S. Pat. Nos. 4,044,404, 4,639,390, 4,657,743, 4,842,505, 5,522,879, 6,106,913 and 6,111,590—all of which feature polymer nanofiber production arrangements.
Electrospinning is a major manufacturing method to make nanofibers. Examples of methods and machinery used for electrospinning can be found, for example, in the following U.S. Pat. Nos. 6,616,435; 6,713,011; 7,083,854; and 7,134,857. In general, electro-spinning is limited mainly due to its low production rate. In many respects centrifugal spinning methods do not suffer the same disadvantages and limitations of electro-spinning techniques.
Centrifugal spinning uses one or more rotating spinnerets to produce nanofibers. Spinning fluid is placed in the rotating spinneret, as either a melt or a solution. The rotation rate of the spinneret is sufficiently high so that centrifugal force overcomes surface tension of the spinning fluid, and a liquid jet is ejected from a nozzle in the spinneret. The jet undergoes a stretching process and forms nanofibers as the jet solidifies. The nanofibers are deposited on a collector such as a substrate disposed below the spinnerets.